RRC Technical Update. EH40 Workplace Exposure Limits 2005 (second edition, published 2011)

Transcription

1 RRC Technical Update EH40 Workplace Exposure Limits 2005 (second edition, published 2011)

2 EH40 Workplace Exposure Limits 2005 Second Edition, published 2011 What is that strange smell? What is that mist in the air? Have you ever asked yourself these questions at work? They re usually followed by wondering if it is likely to cause you any harm... If this sounds familiar, then this update to EH40 contains important information for you! Firstly, you need to find out where the smell or mist is coming from. Once you know that, you can use EH40 to establish whether exposure to it is likely to cause you any harm. EH40/2005 (revised 2011) contains Workplace Exposure Limits - or WELs 1 - which can help you to decide how much of a hazardous substance you can safely be exposed to. In conjunction with COSHH 2, we can then ensure we follow the correct precautions to prevent the harm which can result from over-exposure. This latest thriller does have its drawback of course WELs can only guide us on amounts that we can safely breathe. So if you are one of those clumsy types who spill things or splash them on your skin, it s back to the library, I m afraid! 1 It s worth noting that different terms are used in other parts of the world OEL (Occupational Exposure Limit) is an over-arching term; a WEL is a UK-specific OEL. 2 COSHH is the Control of Substances Hazardous to Health Regulations 2002 (as amended).

3 What is EH40 About? EH40 is all about protecting us from harm. It begins by showing us that substances can cause harm: if we breathe in (inhale) too much of them; if they are absorbed through the skin; if we swallow (ingest) them; or if they act directly on the body at the point of contact, e.g. on contact with the skin. EH40 is concerned with the first method of exposure inhalation. Not all substances are harmful, and many only become harmful once exposure reaches a certain level, so EH40 outlines exactly which substances we need to protect ourselves against. It also details how exposure should be measured so we can gauge current exposure levels. Ill-health caused by exposure (or overexposure) to hazardous substances may take a long time to appear - the symptoms don t always develop immediately. So, knowing how much we can be exposed to before harm will occur can help protect us from harmful exposure to these hazardous substances at work. That s where WELs come in. How does EH40 Work? EH40 contains a comprehensive list of acceptable WELs for 500 different hazardous substances. If a substance is included in this list, then exposure to it must be controlled. Workplace Exposure Limits (WELs) WELs are set for certain substances in order to protect the health of workers. According to EH40: WELs are concentrations of hazardous substances in the air, averaged over a specific period of time, referred to as a timeweighted average (TWA). These averages can be measured across two time periods: long-term exposure limits (LTELs) averaged over 8 hours, and short-term exposure limits (STELs) measured over 15 minutes. STELs can help to prevent such effects as eye irritation, which may happen after just a few minutes exposure, as well as longerterm problems from inhalation. So, to establish the level of exposure in a particular workplace, we can measure over 8 hours (where exposure is constant, but lowlevel) or over 15 minutes (where exposure is less frequent, but in higher concentrations). Once we know of how much of these harmful substances we can safely be exposed to through inhalation, we can begin to consider what to do to ensure these maximums are not exceeded. All substances which are assigned a WEL are subject to COSHH requirements. The effects of hazardous substances can be difficult to identify, but if the substance is included in EH40, exposure to it needs to be controlled.

4 EH40 and COSHH Whenever we re faced with hazardous substances at work, we turn to COSHH for guidance. All substances that have been given a WEL in EH40 must also follow the requirements of COSHH. That means that employers have got to prevent or control exposure of workers to hazardous substances. COSHH tells us that control of exposure has to be adequate, and to be adequate we must apply the principles of good control practice and any WELs shown in EH40 must not be exceeded. Furthermore, if the substance can cause cancer (carcinogens) or cause heritable genetic defects (mutagens), or even asthma, exposure has got to be reduced to as low as reasonably practicable, which is likely to be below the WEL shown in EH40. Even when controls are in place, it s important that a regular monitoring system is used to ensure these controls remain adequate. Scope of the Limits The Workplace Exposure Limits in EH40 (with a few exceptions) relate to personal exposure to hazardous substances that are in the air in the workplace. They are only meant to control exposure for people who are at work. Obviously, the effects of exposure to hazardous substances will depend on the exact nature of the substance and the pattern of exposure (how much we inhale, and for how long). Some effects will not appear straight away, but will need prolonged or accumulated exposure to cause us any harm. The LTEL (8-hour TWA) should control these effects by restricting inhalation over one or more work shifts (depending on the length of the shift). The STEL (15 minute TWA) controls exposure over brief periods, much less than one shift. If a substance doesn t have a STEL its recommended that a figure three times (3 ) the long-term limit is used. Some work tasks are likely to expose a worker to frequent but short exposure periods (less than 15 minutes), but with high levels of contaminant. Even though these may not exceed either the LTEL or STEL, they can still cause harm, and should be adequately controlled. Regular monitoring is required to ensure WELs are not exceeded.

5 How do we Measure the Substance to Determine the Limits? Concentrations of fumes, dust, etc. are usually measured by drawing air containing the contaminant through a filter and measuring what is collected; the amounts are described in mg/m 3. That is how many milligrams of the contaminant there are in every cubic metre of air drawn through the filter. It sounds complicated, but it s actually a very simple idea if you know how much air you ve sampled and how much contaminant you ve collected, you can work out the average concentration of the contaminant in the air. We can also apply the alternative measure of parts per million (ppm) of the sample collected. That is how many contaminant parts there are in every million parts collected. Once you know how much of the contaminant is in the air, you can compare this to the WEL in EH40 to determine whether additional controls are required to reduce exposure to an acceptable level. Other Factors to Consider As well as how much we inhale and the concentration of what we inhale, factors such as exposure to ultra-violet radiation, working in high-temperatures, pressure and humidity can all increase the toxic response to a substance. Absorption Through the Skin WELs are associated with things we can inhale, but some substances also have the ability to get through undamaged skin and become absorbed into the body. Substances that can do this are indicated in EH40 entries as Sk in addition to the WEL. Wearing gloves can help to protect against absorption through the skin Personal/Workplace Air Monitoring COSHH imposes a duty to monitor the exposure of employees to substances hazardous to health in certain specified situations. Sampling strategies may involve measurement of the hazardous substance in the breathing zone of the worker (personal sampling) or in the workplace air. Methods for the sampling and analysis of many substances which have been assigned WELs are described in the HSE series Methods for the Determination of Hazardous Substances (MDHS).

6 Using EH40 Exactly what does the information in EH40 look like? The following table shows some of the information, namely the LTEL and STEL of some of the first (under A ) substances in the list. CAS numbers and comments (such as Sk notations) have been omitted. Substance Extract from Table 1: List of approved workplace exposure limits 8hr LTEL (ppm) 8hr LTEL (mg/m 3 ) 15min STEL (ppm) 15min LTEL (mg/m 3 ) Acetaldehyde Acetic anhydride Acetone Acetonitrile Acrylaldehyde (acrolein) Acrylamide Acrylonitrile Allyl alcohol Aluminium alkyl compounds All in all there are 409 entries in the tables over 19 pages. Mixed Exposures Most of the WELs listed are for single compounds (or compounds with a common radical, such as tungsten and compounds ), or for substances commonly encountered as complex mixtures (such as rubber fume ). These are without prejudice to any WELs for individual components of mixtures. Employers should ensure WELs on safety data sheets are not exceeded.

7 And Finally. Now we know what that strange smell in the workplace is, we can use EH40 to determine its potential for harm and use COSHH to decide what to do about it. References: EH40/2005 Workplace Exposure Limits ISBN Price 15 (UK) downloadable free as a web-friendly version at: Further information can also be found at: